This invention relates to the storage of fluids, and more particularly to methods for loading and unloading different liquids from a liquid transporting vehicle.
When a tank truck or a railroad tank car transporting a particular gas or liquid is to be used to transport a different non-compatible fluid, it is necessary to clean the container of the vehicle. This is usually expensive and inconvenient, and the required specialized cleaning facilities frequently are not available. To solve this problem, it has been proposed that vehicles for transporting fluids be provided with a pair of separate inlets and outlets and a flexible diaphragm that alternately lines opposed sides of the vehicle's container. Movement of the diaphragm to line one side of the container provides a chamber for one fluid, and movement of the diaphragm to the opposite side of the container provides another chamber for a different non-compatible fluid. Thus, the container does not have to be cleaned to enable the vehicle to transport either of such fluids. However, there has not been any significant use of such vehicles having a diaphragm that enables them to alternately carry non-compatible fluids without being cleaned in between. One reason such vehicles have not been used is that the full volumetric capacity of such vehicles was not available for the transportation or storage of fluid. When such vehicles were loaded or unloaded, the flexible diaphragm would not properly line the surface of the vehicle container. The diaphragm would become creased or wrinkled and consequently would not be able to define a liquid storage chamber that includes the entire surface of the container. This would significantly reduce the amount of liquid that could be transported (e.g. by 20%). The usable volume of the container was also reduced when gas or liquid was trapped like a bubble between the flexible diaphragm and the container because of incomplete unloading.